The present invention generally relates to optical head units, and more particularly to an optical head unit which is suited for use in an optical disk unit.
In optical disk units, there are demands to increase the access speed and to reduce the thickness of the optical disk unit. For this reason, it is desirable that the optical head unit have a structure which is unaffected by vibration and is suited for providing high-speed access to information stored in a disk. In addition, it is desirable that the optical head unit have a thin structure.
FIG. 1 shows a first example of a conventional optical head unit. An optical head unit 1 shown in FIG. 1 includes a light emitting part 2 and a light receiving part 3 which are fixedly provided on a substrate. An arm 8 has a built-in parallel prism 5, and an objective lens 6 and a focus actuator 7 are provided at a tip end of the arm 8. This arm 8 is rotated by a motor 4.
A laser beam 9 emitted from the light emitting part 2 is directed towards the parallel prism 5 by a mirror 10, as indicated by 9a. Access to a predetermined track on a magneto-optic disk 11 is made when the motor 4 is driven and the arm 8 is rotated by the motor 4.
On the other hand, FIG. 2 shows a second example of a conventional optical head unit. An optical head unit 20 as shown in FIG. 2 is disclosed in Japanese Laid-Open Patent Application No. 61-261830, for example.
In FIG. 2, an arm 23 is fixed on a shaft 22 of a motor 21. An objective lens 24, a focus actuator 25, a light emitting part 26 and a light receiving part 27 are built into the arm 23. Access to a predetermined track on a disk 28 is made when the motor 21 is driven and the arm 23 is rotated by the motor 21.
However, the conventional optical head units suffer from the following problems.
First, the arms 8 and 23 of the optical head units 1 and 20 both have a relatively long and narrow shape. For this reason, the arms 8 and 23 lack rigidity and easily vibrate, thereby making high-speed access difficult.
Second, it is difficult to make the optical head unit 1 thin because the laser beam 9 travels along a three-dimensional optical path.
Third, it is also difficult to make the optical head unit 20 thin because the arm 23 is fixed on the shaft 22 which projects upwardly from the motor 21.